The problem with the common core approach is that it is busy teach concepts I.e. mathematics instead of teaching arithmetic. Numeration proficiency comes from practice. If any one cares to learn the theory the can take those classes at a higher level
Children of elementary school age don’t and shouldn’t care that 15 can be grouped as 3 sets of 5 or 5 sets of 3. They should know how to do arithmetic. Add subtract multiply and divide correctly and without a calculator.
None of this common core crap is taught at elementary level anywhere else in the world
Actually it very solvable, my wife and I just did it multiple times using different numbers in the middle column. She suggested that all of the middle numbers are multiples of the number in the left column i.e. 15 is divisible by 5. However I solved it using numbers that were prime. It’s doable just ridiculously complicated especially for first and second graders. I believe it is another attempt to do away with absolute truths.